Restriction endonuclease mapping of the Escherichia coli K12 chromosome in the vicinity of the ilv genes

We have determined the EcoRI endonuclease fragment map of the λh80dilv chromosome as well as the EcoRI, HindIII and BamI cleavage patterns of the Escherichia coli chromosome around the ilv genes on F310, F312 and λh80dilv. Comparison of fragment maps from F-prime ilv DNAs with λh80dilv DNA shows the orientation of the bacterial genes on the λh80dilv chromosome. These data, taken together with the results obtained by hybridization of ilv messenger RNA to λh80dilv DNA digested with strand-specific exonucleases, strongly suggest that the ilvOADGE operon is transcribed from a promoter-proximal ilvE to the ilvO gene. This is opposite to the direction of transcription previously reported. The nature of the cis-dominant operator-like mutations that define ilvO remains to be clarified. Hybridization data obtained with EcoRI fragments of the ilv gene cluster indicate that these fragments may be valuable for studying transcription of the individual ilv operons. A model for the fusion of parental F-prime factors F′-lac att⁸⁰trp (F′trp/7) and F′-ilv (F16) is proposed in which recombination and inversion of bacterial DNA between the two copies of the F DNA sequences at position 2.8F to 8.5F allows the formation of a λh80dilv chromosome with the proposed structure.